1. Field of the Invention
This invention relates to servicing a wellbore. More specifically, it relates to servicing a wellbore with a sealing agent that forms a sealant composition in the presence of a nonaqueous fluid.
2. Background of the Invention
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed.
Oil or gas residing in the subterranean formation may be recovered by driving the fluid into the well using, for example, a pressure gradient that exists between the formation and the wellbore, the force of gravity, displacement of the fluid using a pump or the force of another fluid injected into the well or an adjacent well. The production of the fluid in the formation may be increased by hydraulically fracturing the formation. That is, a viscous fracturing fluid may be pumped down the casing to the formation at a rate and a pressure sufficient to form fractures that extend into the formation, providing additional pathways through which the oil or gas can flow to the well. Unfortunately, water rather than oil or gas may eventually be produced by the formation through the fractures therein. To provide for the production of more oil or gas, a fracturing fluid may again be pumped into the formation to form additional fractures therein. However, the previously used fractures first may need to be plugged to prevent the loss of the fracturing fluid into the formation via those fractures.
In addition to the fracturing fluid, other fluids used in servicing a wellbore such as drilling fluids may also be lost to the subterranean formation while circulating the fluids in the wellbore. For instance, the fluids may enter the subterranean formation via depleted zones, zones of relatively low pressure, loss circulation zones having naturally occurring fractures, weak zones having fracture gradients exceeded by the hydrostatic pressure of the drilling fluid, and so forth. The presence of alternative flow pathways in the subterranean formation may make the service provided by such fluids difficult to achieve. In addition, loss of fluids, such as oil-based muds may be quite expensive. Furthermore, the drilling operations may need to be interrupted until the circulation loss problem is solved, which may result in expensive idle rig time.
Formations that are sensitive to water, such as those containing swelling clay and shales, cannot be exposed to water-based fluids because of the potential for sloughing of the formation material into the wellbore. Consequently, such wellbores are typically drilled with oil-based drilling fluids, and loss circulation treatments in such zones may be devoid of any aqueous fluids.
Accordingly, a need exists to develop methods of blocking the flow of fluid through pathways such as fractures filled with water, loss circulation zones in the subterranean formation, voids or cracks in the cement column and the casing, and so forth. A need also exists for a method and composition for use in preventing loss circulation using nonaqueous drilling fluids.